Adder with carry enable for bit operations in an electric digital calculator

ABSTRACT

A greatly simplified calculator circuit implemented, for example, utilizing I 2  L technology is fabricated on a relatively small semiconductor chip resulting in high yield. A unique feature of such calculator is a dual adder which selectively functions as a multibit word adder and also as a plurality of single bit adders. This dual functioning adder cooperates with the calculator system in such a manner as to reduce the total amount of circuitry required to implement the calculator function thereby permitting fabrication on the smaller chip. The dual adder is utilized, for example, to perform bit operations for use in flagging and 2&#39;s complement addition for subtraction operations as well as normal multibit word addition.

This invention relates to calculators and, in particular, to digital electronic calculators fabricated as integrated circuit systems.

Integrated circuit technology has advanced to the stage where an entire calculator system is fabricated on a single chip of semiconductor material including all interface circuitry to an input keyboard, output drivers and display and power supply. These integrated circuit chips have been fabricated, for example, utilizing MOS technology and, more recently, CMOS technology. Reduction of cost in fabricating such integrated calculator systems is directly related to yield. Circuitry embodied in the calculator system of the present invention which is implemented utilizing injection logic I² L technology is directly related to yield in that, by reducing the circuitry required to perform the calculator system function, the chip size is reduced by about 25% and hence the yield increased. The I² L calculator system in addition provides for a lower operating voltage supply of 0.7 volt for the chip and 4.5 for the LED display and provides for the digit drivers to be provided on the single chip.

It is therefore an object of the present invention to provide a greatly simplified calculator circuit on a relatively small semiconductor chip.

It is another object of the invention to provide a semiconductor integrated circuit calculator system in higher yields than presently achieved.

It is still a further object of the invention to provide a bipolar injection logic I² L integrated circuit calculator system.

Still another object of the invention is to provide a dual function wordbit adder in a greatly simplified digital electronic calculator.

These and other objects are provided in accordance with an embodiment of the invention in which a greatly simplified calculator circuit is implemented, for example, utilizing injection logic I² L technology. The integrated circuit calculator system is fabricated on a single relatively small semiconductor chip resulting in low cost and high yield. A unique feature of such calculator permits separation of a multibit word adder into a plurality of single bit adders. This dual function adder reduces the amount of circuitry required to implement the calculator system thereby permitting the fabrication on the smaller chip. The dual function adder is utilized to perform multibit word addition as well as bit operations for use in flagging and 2's complement addition for subtraction operations.

Still further objects and advantages of the invention will become apparent from the detailed description and claims when read in conjunction with the appended drawings wherein:

FIG. 1 is a perspective view of a digital electronic calculator employing the present invention;

FIG. 2 is a block diagram of a digital electronic calculator system embodying the present invention;

FIGS. 3A and 3B comprise a block diagram of the circuitry comprising the digital electronic calculator of FIG. 2;

FIGS. 4A-I form a detailed logic diagram of the calculator system; and

FIG. 5 is a circuit diagram of the digit and segment drivers employed in an embodiment of the calculator system.

This application discloses subject matter related to that disclosed and claimed in the following U.S. patent applications, all filed herewith and assigned to Texas Instruments Incorporated, the assignee of this invention: Serial numbers 527,456, 527,505, 527,507, 527,508, 527,509 and 527,510, all filed on Nov. 26, 1974.

An example of a calculator employing the present invention is illustrated in FIG. 1. The calculator includes a display 12A which has, for example, seven or nine digit positions for the display of a sign and six or eight numeric characters, respectively, and a keyboard 11A comprised of numeric keys 0-9 and function keys such as plus, minus, multiply, divide, equal, clear, etc. The display 12A and keyboard 11A, as well as a power supply 13A, comprised of batteries, for example, and a switch which couples the batteries to the integrated calculator system are shown in FIG. 2. The integrated calculator system 14A is preferably an I² L integrated circuit system fabricated on a single semiconductor chip of relatively small size. The I² L circuitry requires lower operating voltages than MOS or CMOS circuits. For example, the I² L calculator circuits described herein require a system operating voltage of approximately 0.7 volt and the LED display requires an operating voltage of approximately 4.5 volts.

The calculator system is illustrated in greater detail with reference to the block diagram of FIG. 3 comprised of sections 3A and 3B and in still greater detail in the logic diagram of FIG. 4 comprised of sections 4A-I. Referring then to FIGS. 3 and 4, the calculator system is controlled by a programmed ROM 20A which is coupled to and addressed by program counter 19A. Program counter 19A provides a 9-bit address BIT_(O) -BIT₈ to the ROM 20A. The ROM, which in this embodiment, is a five hundred twelve word by eleven bit programmed memory with outputs I_(O) -I₁₀, in conjunction with the other circuitry of the calculator system, causes the system to operate in a particular manner upon activation of each key or sequence of keys from keyboard 11A. An example of a ROM program for the calculator of FIG. 1 is described in Tables I and II.

A single set of digit lines D_(O) -D₆ are utilized to multiplex the display and to scan the keyboard. During the normal display, every digit line D_(O) -D₆ is scanned and every key input line K₁ -K₄ is sensed by the key latch 17A. The key latch 17A is comprised of cross-coupled NAND gates 804 and 805 and receives inputs from the key input lines K₁ -K₄ via NAND gates 800, 1202 and 1203. By means of the instruction "test key" which is also fed into the universal condition latch 15A, at the end of every six digit times, the key latch is tested to determine whether a key is being actuated or not.

In order to compensate for key bounce which is typically about 8 milliseconds, the ROM program causes testing of the key latch 17A three consecutive times to insure that a key is actually being actuated. Scanning at, for example, 72 instructions per cycle provides for approximately a 5 millisecond delay. After the key latch 17A has been tested for the third time, and it is determined that the key latch is still latched, the digit lines beginning with D₆ are scanned and each K line is individually tested during each digit time until a positive test sets the universal condition latch 15A.

The universal condition latch 15A, comprised of cross-coupled NAND gates 60 and 71, is a unique feature of the calculator system described herein. In prior art calculators, a condition latch was utilized to test the results of a compare operation and/or the carry from the arithmetic unit. The state of the universal condition latch disclosed herein is additionally set by the logical OR of up to four flags in the RAM after a test flag instruction, testing of the RAM for other purposes such as for all 0's, and testing the logical OR of the keyboard input lines K₀ -K₃ after a test key instruction. These additional inputs provided to the universal condition latch circuitry 15A saves a large number of instructions and contributes to the smaller high yield chip where the calculator system is implemented as an integrated circuit. The universal condition latch will later be referred to with respect to the memory test, flag test, carry output, compare and other operations carried out utilizing the universal condition latch. Referring to FIG. 4, the key input lines K₁ -K₄ are coupled to the universal condition latch by means of NOT gates 810-813, 56-59, NAND gates 49-52, and NAND gate 53. The output of gate 53 is the logical OR of the key inputs K₁ -K₄ as controlled by gates 45, 46, 55 and 54.

A positive test determines which of the keys is actuated and the ROM causes the calculator to act according to the actuated key. For example, if a numerical key is being actuated, the condition latch 15A is set (in this particular instance to a "0") and the subroutine register 18A, by means of the branch and call logic 16A coupled to the universal condition latch 15A, cause a branch to the number entry routine and enters the number, corresponding to the actuated key, in the next location in RAM 25A. Where the actuated key is a function key, the condition latch 15A is set to a logical "0" and the subroutine register branches to the particular routine to carry out the function for that actuated key. A digit time D₁, the key latch is disabled and reset. As can be seen from the above description, utilization of the universal condition latch 15A and key latch 17A coupled to the key input lines K₁ -K₄ provides for less ROM lines to decode an actuated key. Utilization of the key latch avoids the necessity of testing each individual K line during each normal cycle. The use of the universal condition latch circuitry avoids the necessity of a programmed logic array which is utilized in prior art calculators in conjunction with additional programming.

The output of the condition latch circuitry 15A is connected to the branch and call logic circuitry 16A. The branch and call logic circuitry 16A includes gate 221 which circuitry determines whether the instruction is a branch or a call instruction and also checks the condition of condition latch 15A to determine whether it is set to a logical "1" or "0". If condition latch 15A is set to a logical "1" the branch or call is executed; if it is set to a logical "0" it is not executed. With condition latch 15A set to a logical "1", gate 897 is forced to input the instruction word ROM address BIT₀ -BIT₈ which is the new location to branch to or call to into the program counter 19A. The ROM instruction branch or call has two bits I₉ and I₁₀. A logical "1" in I₁₀ determines that the instruction is a branch or a call instruction and a logical "1" in I₉, in conjunction with a logical "1" in I₁₀, determines that it is a call rather than a branch. If the instruction is a call instruction, then a logical "0" output is provided for gate 221; if it is a branch or a call, a logical "1" at the output of gate 229 and if it is a call, then a logical "1" appears on ROM output line I₉ to the input of gate 13 along with the logical "1" from gate 229. Thus, under normal conditions each of the stages of the subroutine register 18A, comprised of a set of gates B₁ -B₄ for each stage, is loaded with the information contained in a previous program counter stage comprised of a set of gates A₁ -A₄ for each stage so that the next address from that contained in program counter 19A is normally being stored in subroutine register 18A. When a call occurs, the "load subroutine register" latch, comprised of gates 14 and 15, disables the normal loading of the subroutine register 18A. A branch to the new location occurs and, at the same time, the address of the location that next would have been executed is saved in subroutine register 18A. Thus, in the call mode, the output of gate 14 is coupled to return gate 223. If a return instruction is decoded, then the output of gate 223 goes to a logical "0" and through paths 228 and 230 forces the program counter to be set to the location stored in the subroutine register (via gate A₆ on all stages). After that is accomplished, it allows the subroutine register to return to its normal state and begin loading a new address from the program counter 19A. Every call after the initial call is treated as a branch by the called program in order to save words in the program. Thus, if a call appears within a call, the program returns to the initial return address; this is the same as a branch.

A power up clear latch 21A comprised of cross-coupled NAND gates 17 and 18 are coupled to program counter 19A by means of gate 19 and program counter 19A is coupled back to the power up clear latch 21A through reset NAND gate 16.

The power up clear latch is another unique feature of the disclosed calculator which provides power up clear to reset the calculator to a "0" idle state when the calculator power, provided by power supply 13A, is initially switched on. The power up clear latch 21A disclosed herein is smaller and more reliable than the conventional open loop power up clear circuits which rely entirely on an RC time constant. Elimination of the relatively large capacitor and other associated circuitry contributes to the fabrication of the present system on the smaller semiconductor chip. The power up clear latch comprised of cross-coupled gates 17 and 18 forces the input to the program counter 19A at the output of gate 19 to a logical "1". This causes program counter 19A to increment. When an initial logical state is reached, as indicated by the output of the program counter (in this embodiment all logical 1's), the logical NAND gate 16 coupled to the program counter outputs causes the power up clear latch to be reset.

In the preferred I² L embodiment, the gates A13 and 18 automatically and accurately power up low (logical "0") when the power is turned on. This is accomplished by increasing the size of the injectors of gates A13 and 18 relative to those of 14 and 17. The injectors are made larger by approximately a factor of 4 so that when the power is turned on, the output of gate 18 is a logical "0", the output of gate 19 is a logical "1", and each stage of the program counter will, in turn, change to a logical "1". In other MOS or bipolar embodiments, a relatively small capacitor may be utilized in lieu of the enlarged gates to power the gates up in a particular logic state. When all of the stages of the program counter have changed to logical 1's, gate 16 resets the latch comprised of gates 17 and 18 on the next phase 2 clock pulse and the ROM address is set at an initial IFF ready to accept the first key entry.

Flag data stored in random access memory 25A is tested by flag test circuitry 22A comprised of NAND gates 40-44. Gates 40-43 provide the logical OR of up to four flags at the output of gate 44 which is utilized to set the condition of universal condition latch 15A after a test flag instruction. NAND gate 44 is coupled to condition latch gates 60-71 by means of gates 47 and 53. Gate 47 is enabled by the decoding of a test flag instruction from ROM outputs to gates 45-47.

Random access memory 25A, in this particular embodiment, is 28 locations by 4 bits addressed by a 5-bit address word provided by means of address selector 26A. The address selector 26A is a unique feature of the calculator system described herein in that both direct and indirect RAM addressing is provided while the number of ROM instructions required for calculator operation is reduced. Thus, by reducing the number of ROM instructions required, the direct and indirect addressing feature contributes to a reduced size of the ROM to permit fabrication on the smaller semiconductor chip. Address selector 26A includes inputs RA₀ -RA₃ from the RAM address register 33A to apply the address stored in the RAM address register to an input of NAND gates 192, 189, 186, and 183. The first four bits of the instruction word from ROM 20A is applied to an input of NAND gates 190, 188, 184 and 182. NAND gates 191, 187, 185 and 181 provide the first four bits of the RAM address as either the contents of the RAM address register 33A or the first four bits of the instruction (I₀ -I₃) contained in the addressed ROM word depending upon the logical state of the seventh (I₆) bit of the instruction word contained in the ROM. The state of instruction bit I₆ enables either the set of gates 192, 189, 186 and 183 or the set of gates 190, 188, 184 and 182. The fifth bit of the RAM address is always provided by the fifth bit (I₄) of the ROM instruction word.

Indirect addressing, that is, enabling RAM address selector 26A to select the address from RAM address register 33A, is particularly useful for register type adds or shifts where it is desired to use the exact same instruction from the ROM but with the address of the RAM incremented by one so as to perform the exact same function to each of a series of digits by incrementing from digit to digit. Thus, for example, a particular operation such as adding digits or shifting may be accomplished by initializing the RAM address to 0, performing the function on digit 0, incrementing the RAM address register and then testing to determine if the RAM address register has reached the last digit (for example, digit 7). If the RAM address register does not contain a 7, the operation is performed on the addressed digit (which in this case would be digit 1). The digit is then incremented, tested for last digit, function performed, incremented, etc. Direct addressing, on the other hand, provides for addressing of the RAM by the permanently stored contents of the first five bits of the ROM instruction. By the use of a single location in the ROM, an operation is performed on eight or nine different digits, for example, providing in essence the equivalent of eight or nine different instructions. By utilization of the indirect addressing feature, the number of ROM instructions is thereby decreased. Additionally, the direct addressing is directly from the ROM without disturbing the contents of RAM address register 33A. A location does not have to be extracted from the ROM and loaded into the RAM address register to indirectly address the RAM 25A by means of RAM address register 33A as is done in some prior art calculators. Testing operations are therefore conveniently carried out by utilization of the direct addressing feature. For example, while the RAM address register is incrementing from digit to digit, the ROM word may be utilized to directly address some known location like the location of the first digit without disturbing the contents of the RAM address register. The contents of the RAM address register does not have to be temporarily stored, reset and restored.

A further example of the use of the direct and indirect addressing feature is illustrated with respect to the multiply routine in which the final digit is checked and a binary one is continually subtracted from the least significant digit in the multiplier and the multiplicand is continually added to the partial product. Once the least significant digit becomes a 0, the partial product multiplicand and multiplier are shifted and the operation continues on the next digit with the adding of the multiplicand to the partial product. Each time the least significant digit of the multiplier is to be checked, the least significant digit is directly addressed without affecting the contents of the RAM address register 33A from which a one is continually being subtracted. In division, a one is continually added to the quotient and, as long as the dividend can be subtracted from the divisor, directly puts the result in the accumulator, adds one to it, and returns the result without changing any of the address selects.

The direct and indirect addressing feature is also particularly useful in the display cycle, saving additional ROM memory locations. During the display cycle, in order to light up the decimal point, for example, the condition latch 15A is set to a particular logical level (logical "0" ) and two instructions take place before a load output. With direct addressing, the digit being scanned is stored in the accumulator, compared to the decimal point value, which value is determined by directly addressing the memory at the decimal point location, and on the next instruction taking the next digit to be displayed in the particular D time by indirectly addressing RAM 25A from the RAM address register 33A and storing the digit in the accumulator. On the next instruction "load output" the correct D time is stored in RAM address register 33A and the correct digit has been loaded in accumulator register 34A.

Another unique feature of the calculator system is the particular structure of the adder 30A. The adder 30A is comprised of four 1-bit adders 32A-D. Each 1-bit adder includes first and second half adder stages as shown in FIG. 4G. The first half adder stage of first 1-bit adder section 32A is comprised of NOT gate 103 which receives the first A input bit from A input selector 27A, NOT gate 108 which receives the first B input bit from B input selector 28A, NAND gates 104-106 which add the first A input bit to the first B input bit, and NOT gate 107 which transfers the carry to the second half adder stage of second 1-bit adder 32B. In this particular embodiment, first adder section 32A does not include a second half adder stage and the output from NAND gate 106 is applied directly to an output latch comprised of NOT gate 602 and NAND gates 194-197 which store the adder output during a phase 1 clock pulse. A carry input is omitted because it eliminates about six gates thereby contributing to the reduced size of the semiconductor chip. The input carry function is provided by the ROM instruction which adds a one to any constant of the accumulator when it is loaded. The first half adder stage of second 1-bit adder section 32B is comprised of NOT gate 109 which receives the second A input bit from A input selector 27A, NOT gate 117 which receives the second B input bit from B input selector 28A, NAND gates 110-112 which add the second A input bit to the second B input bit, and NAND gate 141 which transfers the C₂ carry to the second half adder stage of third 1-bit adder section 32C. The second half adder stage of second 1-bit adder section 32B includes NAND gates 142-143 and NOT gates 145 and 146 which add the C₁ carry applied from NOT gate 107 of first adder section 32A when NAND gate 147 is enabled in accordance with the logical state of instruction bit 5 (I₅) from ROM 20A. The first half adder stage of third 1-bit adder section 32C is comprised of NOT gate 116 which receives the third A input bit from A input selector 27A, NOT gate 118 which receives the second B input bit from B input selector 28A, NAND gates 113-115 which add the third A input bit and the third B input bit and NAND gate 134 which transfer the C₄ carry bit to the second half adder stage of fourth 1-bit adder section 32D. The second half adder stage of third adder section 32C is comprised of gates 135-139 which add the C₂ carry applied from NAND gate 141 of second adder section 32B when NAND gate 140 is enabled in accordance with the logical state of instruction bit 5 as discussed with respect to NAND gate 147. The first half adder stage of fourth 1-bit adder section 32D includes NOT gate 119 for receiving the fourth A input bit from A input selector 27A, NOT gate 123 for receiving the fourth B input bit from B input selector 28A, NAND gates 120-122 for adding the fourth A and B input bits, and NAND gate 124 for generating the C₈ carry output. The second half adder section of fourth adder section 32D is comprised of gates 128-133 which add the C₄ carry from adder section 32C. NAND gate 133 is enabled in accordance with the logical state of instruction bit 5 from ROM 20A and operates in the same manner as gates 140 and 147. The output latch of adder sections 32B-D are identical to the output latch of section 32A. Thus, adder 30A comprised of sections 32A-D including carry C₁ from section 32A to 32B carry C₂ from section 32B to 32C and carry C₄ from section 32C to 32D when a logical "1" enable signal is applied to NAND gates 133, 140 and 147 by instruction bit 5 from ROM 20A. If instruction bit 5 is a logical "0" NAND gates 133, 140 and 147 disable the carries from adder section to adder section so that the adder sections 32A-32D operate as individual non-carry 1-bit adders. In this manner, adder 30A selectively functions dually as a multi-bit word adder and also as a plurality of single bit adders. The dual function adder is utilized, for example, to perform bit operations for use in flagging and 2's complement addition for subtraction operation as well as normal multi-bit word addition. With the carry disabled, a "1" can be added to any bit without having it carry bit to bit so that selected bits are toggled individually by adding "1" to those bits. Flags are toggled in this manner. For example, utilizing indirect addressing, a particular RAM address is selected by RAM address register 33A. The RAM data applied to the A input selector 27A is added to selected binary 1's from first 4 bits of the ROM instruction word applied through B input selector 28A with the carry disabled by instruction bit 5 to selectively and individually toggle one or more flags. The altered RAM flag data is then returned to the RAM at the same address without the contents of the accumulator being altered.

Disabling of the carry is also utilized in this embodiment to perform subtraction utilizing 2's complement as indicated above. In order to generate the 2's complement of the data in the accumulator, a numerical 15 from a ROM instruction at the A input selector 27A is added to the contents of the accumulator transferred through B input selector 28A with carry enable gates 133, 140 and 147 disabled by bit 5 of the instruction. In this manner every bit of the accumulator is toggled and a one is added to the results to obtain the 2's complement. Feedback of the complement of the accumulator and the carry is not required thereby reducing the number of interconnects and selector gates on the front end of the adder and contributing to the smaller sized chip. Adder 30 also includes NAND gate 148 for performing a compare of the outputs from the first adder stages to generate a C compare output to condition latch 15A.

As previously mentioned, there are A and B inputs to the adder with the A input provided by A input selector 27A and B input provided by B input selector 28A. A input selector 27A selects as the A input to adder 30A either the 4-bit data from the RAM (MEM1, MEM2, MEM4, MEM8) or the first 4 bits of the ROM instruction (I₀ -I₃) depending upon the state of instruction bit 7. The A input selector is comprised of NAND gates 100-102 for selection of the first bit, NAND gates 97-99 for selection of the second bit, NAND gates 94-96 for selection of the third bit, and 91-93 for selection of the fourth bit to adder 30. B input selector 28A selects as the B input to adder 30A either the 4-bit output of RAM address register 33A (RA₀ -RA₃) or the four bits of accumulator 24A (ACC₁, ACC₂, ACC₄, ACC₈) depending upon the logical states of ROM bits 6 and 7 to NAND gate 180 to NOT gate 179. The input selector 28A includes NAND gates 167-169 for selection of the first bit, NAND gates 170-172 for selection of the second bit, NAND gates 173-175 for selection of the third bit and 176-178 for selection of the fourth bit to adder 30.

Zero selector 29A comprised of NAND gates 163-166 couples B input selector 28A to the B inputs of adder 30A. The zero selector provides for the generation of all zeros at the B adder inputs in order to load a constant from the ROM by means of A input selector 27A to the A adder inputs. The zeros are generated when the instruction bit 9 to gates 163-166 is a logical "1". .

The 4-bit output Y from adder 30A, which does not include the carry output C₈, is stored in either RAM address register 33A or accumulator register 34A. In general, RAM address register 33A is utilized to store RAM addresses as previously discussed with respect to indirect addressing. Four identical sections are provided, one corresponding to each of the adder sections, to store the 4 bits. Each of the sections is comprised of a latch such as that provided by cross-connected NAND gates 199 and 200 shown for the first section and input gates such as NAND gates 198 and 201 also shown only for the first section. The input gates 198-201, etc. are controlled by the load address register enable signal (LDR) generated by instruction decoder NAND gates 149-151. Decoder NAND gates 149-151 decode selected bits from the instruction word and generate the LDR enable signal so that the adder output is loaded into RAM address register 33A for instructions which cause the calculator system to operate on RAM addresses. The outputs RA₀ -RA₃ of RAM address register 33A are coupled to RAM address selector 26A for providing the RAM address to RAM 25A when indirect addressing is selected by instruction bit 6 to RAM address selector 26A. The outputs RA₀ -RA₃ are also fed back to B input selector 28A to adder 30A so that the RAM address may be selectively incremented by the adder. The output bits from the four adder sections 32A-32D are also coupled to accumulator register 34A as indicated above for storing all other data received from the adder. Each section of accumulator register 34A is identical and comprised of two cross-coupled NAND gates such as 203 and 204 shown only for the first section and two input gates such as 202 and 205 also shown only for the first section. The input gates 202 and 205 transfer the data from the adder outputs to the latch as controlled by the load accumulator enable signal (LDA) transferred from decoder NAND gates 814, 125 and 126 up to the gates 202, 205, etc. by means of NOT gates 127. The decoder gates 814, 125 and 126 are coupled to and decode selected bits of the ROM instruction so that the input gates of the accumulator are enabled for all instructions requiring the adder output to be stored in the accumulator register 34A. The output bits ACC₁, ACC₂, ACC₄ and ACC₈ from accumulator register 34A are coupled to the corresponding bits of the RAM data input (BIT1, BIT2, BIT4 and BIT8, respectively) for the storage of data in RAM 25A. The accumulator outputs ACC₁, ACC₂, ACC₄ and ACC₈ are also fed back to adder 30A by means of B input selector 28A so that additional operations are carried out on data stored in accumulator register 34A by adder 30A.

The ACC₁, ACC₂, ACC₄ and ACC₈ accumulator register outputs are also coupled to segment decoder 35A. Segment decoder 35A is illustrated in detail in FIG. 4C as a programmed logic array which accepts the 4-bit binary or binary coded decimal output of accumulator register 34A, stores it in latches and converts it to one of, for example, 7 segments SA-SG. The SH or DP output is provided for the decimal point. The segment decoder of the illustrated embodiment is unique in that the segment outputs are latched at the output to the programmed logic array. Latching of the segments allows the display to be continuous during the time in which the calculator is performing other operations. Latching of the decoder at its input rather than at its output reduces the number of gates and latches required to perform the function thereby contributing to the smaller size of the higher yield semiconductor chip. NAND gates 870, 873 and NOT gate 874 input the first bit from the accumulator which is stored in the first latch comprised of cross-coupled NAND gates 871 and 872. Gates 870A-874A provide the same function for the second bit, gates 870B-874B for the third bit, and gates 870C-874C for the fourth bit. The output section is comprised of NAND gates 829-846 with inverter drivers S₁ -S₁₇ for the segment outputs SA-SH.

Digit scanning is provided in the present embodiment by the output state of the three output bits RA₀ -RA₂ of RAM address register 33A which is decoded by digit decoder 36A. Digit decoder 36A stores the three bits and decodes them into one of six, seven or eight unique digit output signals D₀ -D₆. The first bit from the RAM address register is input to NAND gate 870F and NOT gate 874F to NAND gate 874F and stored in the latch comprised of cross-coupled NAND gates 871F and 872F. Gates 870E-874E provide the same function for the second bit and gates 870D-874D for the third bit. The latches allow a digit output to be on while the calculator is performing other operations and are provided for the same reason as the input latches to the segment decoder 35A. NAND gates 817-825 and 847-848 provide the unique digit line outputs from the digit decoder 36A to the inverter drivers 1D-21D for digit outputs D₀ -D₆.

In the preferred I² L single chip integrated circuit embodiment of the described calculator system, the inverter drivers 1S-17S and 1D-21D are of the grounded emitter type. The segment drivers 8S-14S and 17S are shunt type drivers as illustrated in FIG. 5. Each of the light emitting diode segments of each digit such as L₁ is coupled to the digit line associated with that particular digit D₀, D₁, D₂, etc. and to the common segment line for that particular segment SA, SB, SC, etc. The digit drivers 15D, 16D, 17D, etc. each include an emitter grounded transistor Q₂. The segment drivers 8S, 9S, 10S, etc. each include an emitter grounded transistor Q₁, a shunt resistor R₂ and a load resistor R₁ with load resistor R₁ coupled to power supply 13A (VCC). To turn off the segment, transistor Q₁ pulls the voltage down at node N₁ to the point where the light emitting diode L₁ is not forward biased. It required more current to keep the light emitting diode L₁ turned off than it does to drive the diode L₁. In accordance with the described embodiment, in order to reduce the current drawn by those drivers for which the segment is turned off, whenever all segments of a particular digit are blank, the digit driver is turned off (even if it would otherwise be time for that particular digit to be on) and all of the segment drivers are turned off. In that manner, no current flows through resistors R₁ and R₂ because the digit is off and the segment driver is off thereby conserving a considerable amount of power for blank digits.

With the above scheme, for blank digits, all segments are allowed to be on but the digit line turned off, instead of the normal mode in which the digit line is turned on and the segments are turned off. Without the digit outputs D₀ -D₆ being turned on for the blanked digits, the keyboard 11A is checked only by means of the special automatic blanking circuit of 38A. The automatic blanking circuit switches back to the normal mode for one half of an instruction cycle out of twelve, for example, instruction cycles per D (digit) time for the key input to be tested.

The autoblanking, minus sign and decimal point latch circuitry 38A is shown on FIG. 4B and provides several unique functions for the calculator. The segment decoder, in addition to decoding the segments, decodes a 15 (1111) to determine whether the digit is blank and generates a BLANK signal to NAND gate 910 of automatic blanking circuit 38A. A disable latch comprised of NAND gates 887 and 888 is controlled by the BLANK signal to NAND gate 910 and also by inputs from NAND gates 889, 890 and 1202. A disable signal is applied to NAND gate 815 and NOT gate 816 by the disable latch to block all segment outputs SA-SG at the output side of the segment decoder PLA and block all digit outputs D₁ -D₆ at the output side of the digit decoder PLA thereby providing blank digits to the display 12A in the minimum power mode.

Gates 890 and 891 decode selected instruction bits and gate 889 detects a phase 1 clock pulse (φ₁) so that on the first phase 1 clock pulse of a load output instruction the digit line is activated as in the normal mode and all segment outputs are forced to their load state so that the display is blank for a blank digit due to the segments being blank. During this same half clock pulse, the key latch comprised of NOT gate 802 and NAND gates 803-805 is enabled to be set if a key is actuated. Then, at the phase 2 clock pulse which is detected by one input of NAND gate 910, if the digit is not D₆ (indicating a possible minus sign) and the digit is a blank as indicated by the BLANK signal, the output of gate 910 causes latch 887, 888 to shut off all of the digit and segment outputs so that the drivers are drawing no current for the next eleven instruction cycles to take place during the particular D time.

Circuitry 38A also includes a minus sign latch comprised of NAND gates 893-901 which is set by negative numbers and a decimal point latch comprised of NAND gates 902-905.

NAND gates 806-808, 822, 24, 26, and 28 provide means for directly outputting the contents of RAM 25A, condition latch 17 and ROM instruction bits 8-10 via digit decoder gates 848-853 for test purposes. This is accomplished by providing a test enable signal (T) to terminal T₁₄. In a like manner, the test enable signal enables gates 840-846 of segment decoder 35A to output ROM instruction bits 0-7 for test purposes.

The I² L calculator system as described above is controlled by a two phase clock system provided by oscillator 40A. The oscillator is comprised of inverter gates C1-C25, NAND output gates C27 and C28, and output inverter gates C29-C34. The inverter gates C1-C25 are an odd number so that the logic level of gate C27, for example, goes to one at the input from gate C1 when the pulse is at gate C1. When the pulse reaches gate C14, gate C27 is switched to zero. The pulse continues to travel around the loop to gate C1 again and gate C27 is switched back to a logical "1" thereby providing clock pulses of phase 1 (φ₁). Gate C28 which operates in a similar manner is out of phase with the first phase clock pulses, receiving its input from gates C2 and C7 to produce the clock pulses of the second phase (φ₂).

As mentioned previously, the calculator system operates in accordance with a program stored in ROM 20A. The instruction set for the illustrated embodiment of the calculator system is given in Table I. An example of a specific program for the four function calculator illustrated in FIG. 1 is given in its entirety in Table II.

                                      TABLE I                                      __________________________________________________________________________     INSTRUCTION SET                                                                ROM CODE                                                                                                                   Action and                         Mnemonic                                                                             I.sub.10                                                                           I.sub.9                                                                           I.sub.8                                                                           I.sub.7                                                                           I.sub.6                                                                           I.sub.5                                                                           I.sub.4                                                                            I.sub.3                                                                           I.sub.2                                                                           I.sub.1                                                                           I.sub.0                                                                              Description                        __________________________________________________________________________     AKRA  0   1  0  0  1  1  1   K.sub.8                                                                           K.sub.4                                                                           K.sub.2                                                                           K.sub.1                                                                           K+RAMAD→RAMAD -                                                         A four bit constant K.sub.8                                                    -K.sub.1                                                                       is added to the contents                                                       RA3-RA0 of RAM address                                                         register 33A and the results                                                   stored in register 33A. If                                                     a carry output (C8) is pro-                                                    duced condition latch 15A                                                      is set to 0 for one instruction                                                cycle.                                AKAC  0   1  0  0  0  CE 0   K.sub.8                                                                           K.sub.4                                                                           K.sub.2                                                                           K.sub.1                                                                           K+ACC→ACC - A four bit                                                  constant K.sub.8 -K.sub.1 is                                                   added to                                                                       the contents ACC.sub.8 -ACC.sub.1                                              2                                                                              of accumulator register 34A                                                    and the results stored in                                                      register 34A. CE is adder                                                      carry enable; 1 = enable.                                                      If a carry (C8) is produced                                                    condition latch 15A is set                                                     to 0 for one instruction                                                       cycle.                                CKRA  0   1  1  0  1  0  0   K.sub.8                                                                           K.sub.4                                                                           K.sub.2                                                                           K.sub.1                                                                           K=RAMAD - A four bit                                                           constant K.sub.8 -K.sub.1 is                                                   compared                                                                       to the contents of RAM                                                         address register 33A. If                                                       they compare (C) condition                                                     latch 15A is set to 0 for one                                                  instruction cycle.                    CKAC  0   1  1  0  0  0  0   K.sub.8                                                                           K.sub.4                                                                           K.sub.2                                                                           K.sub.1                                                                           K=ACC - A four bit constant                                                    K.sub.8 -K.sub.1 is compared to                                                the                                                                            contents of accumulator                                                        register 34A. If they com-                                                     pare (C) condition latch                                                       15A is set to 0 for one                                                        instruction cycle.                    LKRA  0   0  0  0  1  0  1   K.sub.8                                                                           K.sub.4                                                                           K.sub.2                                                                           K.sub.1                                                                           K→RAMAD - A four bit                                                    constant K.sub.8 -K.sub.1 is                                                   stored                                                                         in RAM address register                                                        33A.                                  LKAC  0   0  0  0  0  0  0   K.sub.8                                                                           K.sub.4                                                                           K.sub.2                                                                           K.sub.1                                                                           K→ACC - A four bit con-                                                 stant K.sub.8 K.sub.1 is stored                                                in                                                                             accumulator register 34A.             LKAR  0   0  0  0  1  1  1   K.sub.8                                                                           K.sub.4                                                                           K.sub.2                                                                           K.sub.1                                                                           K→RAMAD; K→ACC -                                                 A four bit constant K.sub.8                                                    -K.sub.1                                                                       is stored in both RAM                                                          address register 33A and                                                       accumulator register 34A.                                                      MEM+ACC→ACC                    AMAC  0   1  0  1  ADS                                                                               1  R.sub.16                                                                           R.sub.8                                                                           R.sub.4                                                                           R.sub.2                                                                           R.sub.1                                                                           The contents of RAM 25A                                                        at a specified address is                                                      added to the contents of                                                       accumulator register 34A                                                       and the results are stored                                                     in register 34A. If a                                                          carry (C8) is produced                                                         condition latch 15A is set                                                     to 0 for one instruction                                                       cycle. *The specified                                                          address is R.sub.16 -R.sub.1 if                                                ADS                                                                            is 1 (direct address) or                                                       R.sub.16, RA3-RA0 if ADS is                                                    0 (indirect address).                 CMAC  0   1  1  1  ADS                                                                               0  R.sub.16                                                                           R.sub.8                                                                           R.sub.4                                                                           R.sub.2                                                                           R.sub.1                                                                           MEM=ACC - The contents                                                         of RAM 25A at a specified                                                      address* is compared to                                                        the contents of accumulator                                                    register 34A. If they com-                                                     pare (C) condition latch                                                       15A is set to 0 for one                                                        instruction cycle.                    MTOA  0   0  0  1  ADS                                                                               0  R.sub.16                                                                           R.sub.8                                                                           R.sub.4                                                                           R.sub.2                                                                           R.sub.1                                                                           MEM→ACC - The contents                                                  of RAM 25A at a specified                                                      address* is stored in                                                          accumulator register 34A.             ATOM  0   1  1  1  ADS                                                                               1  R.sub.16                                                                           R.sub.8                                                                           R.sub.4                                                                           R.sub.2                                                                           R.sub.1                                                                           ACC→MEM - The con-                                                      tents of accumulator                                                           register 34A is stored in                                                      RAM 25A at a specified                                                         address*.                             EXAM  0   0  0  1  ADS                                                                               1  R.sub.16                                                                           R.sub.8                                                                           R.sub.4                                                                           R.sub.2                                                                           R.sub.1                                                                           MEM⃡ACC - The con-                                                 tents of accumulator                                                           register 34A and the con-                                                      tents at a specified                                                           address* of RAM 25A are                                                        exchanged.                            MTRA  0   0  1  1  ADS                                                                               0  R.sub.16                                                                           R.sub.8                                                                           R.sub.4                                                                           R.sub.2                                                                           R.sub.1                                                                           MEM→RAMAD - The                                                         contents of RAM 25A at                                                         a specified address* is                                                        stored in RAM address                                                          register 33A.                         BRNC  1   0  A.sub.8                                                                           A.sub.7                                                                           A.sub.6                                                                           A.sub.5                                                                           A.sub.4                                                                            A.sub.3                                                                           A.sub.2                                                                           A.sub.1                                                                           A.sub.0                                                                           BRANCH if condition latch                                                      is equal to 1. A.sub.8 -A.sub.0                                                is                                                                             the branch address.                   CALL  1   1  A.sub.8                                                                           A.sub.7                                                                           A.sub.6                                                                           A.sub.5                                                                           A.sub.4                                                                            A.sub.3                                                                           A.sub.2                                                                           A.sub.1                                                                           A.sub.0                                                                           CALL if condition latch is                                                     equal to 1. A.sub.8 -A.sub.0 is                                                the                                                                            call address.                         RETN  0   0  1  0  1  1  0   0  0  0  0  RETURN if in CALL mode,                                                        otherwise NO-OP.                      TSTF  0   0  1  0  0  0  R.sub.16                                                                           F.sub.4                                                                           F.sub.3                                                                           F.sub.2                                                                           F.sub.1                                                                           Test Flag - F.sub.4 -F.sub.1                                                   are                                                                            flag test select bits. A                                                       flag test is performed on                                                      each bit of a RAM word                                                         at a specified location                                                        for which the select bit                                                       is a 1. Any bit or the                                                         logical OR of any com-                                                         bination of bits selected                                                      by the flag test select                                                        bits of the addressed                                                          RAM word are tested.                                                           The specified location                                                         is, in this instance,                                                          always the indirect                                                            address R.sub.16, RA3-RA0.            TSTK  0   0  1  0  1  0  0   K.sub.4                                                                           K.sub.3                                                                           K.sub.2                                                                           K.sub.1                                                                           Test Key Line -                                                                K.sub.4 -K.sub.1                                                               are the key line select                                                        bits. Any key line can                                                         be tested. If the test is                                                      true, condition latch 15A                                                      remains 1. For a special                                                       TSTK instruction (TSTKF)                                                       in which I.sub.3 -I.sub.0 =                                                    1111, the                                                                      key latch is checked. If                                                       the key latch is set to 1,                                                     it indicates a key being                                                       detected since the last                                                        TSTKF instruction and                                                          condition latch 15A is                                                         set to 0 for one instruc-                                                      tion cycle. -LOUT 0 0 1 0 1 1 1 1                                              10 0 0 Load Outputs                   SMIN  0   0  1  0  1  1  0   1  0  0  0  Set Minus Sign                        __________________________________________________________________________                                              Latch                            

                                      TABLE II                                     __________________________________________________________________________     Example of ROM Program                                                         ROM                                                                            Address                                                                             Instruction                                                                              Statement                                                                            Source Statement                                          __________________________________________________________________________     000  0000111 1111                                                                             0072  TCFFDIS LKAR    15                                        001  001011 11000                                                                             0073          LOUT           TURN OFF DISPLAY                   002  0000101 1010                                                                             0074          LKRA    10                                        003  001011 00000                                                                             0075          RETN                                              004  0000111 0000                                                                             0076  PUP     LKAR    0                                         005  011101 0 0000                                                                            0077  PUP1    ATOM0                                             006  0100111 0001                                                                             0078          AKRA    1                                         007  10 000000101                                                                             0079          BRNC    PUP1                                      008  001011 00000                                                                             0080          RETN                                              009  011101 1 0000                                                                            0081  PUP2    ATOM1                                             00A  0100111 0001                                                                             0082          AKRA    1                                         00B  10 000001001                                                                             0083          BRNC    PUP2                                      00C  0000101 1000                                                                             0084  LOCK1   LKRA    8                                         00D  001000 1 0001                                                                            0085          TSTF1   F1                                        00E  11 000011011                                                                             0086          CALL    TOGF1                                     00F  0000000 1000                                                                             0087  LOCK    LKAC    8                                         010  011111 0 0111                                                                            0088          ATOMD0  7                                         011  0000111 1110                                                                             0089  NOLOCK  LKAR    14                                        012  0000000 0110                                                                             0090          LKAC    6                                         013  011111 0 0110                                                                            0091  PDIS1   ATOMD0  6                                         014  0000000 1111                                                                             0092          LKAC    15                                        015  011101 0 0000                                                                            0093          ATOM0                                             016  0100111 1111                                                                             0094          AKRA    15                                        017  010111 0 0110                                                                            0095          AMACD0  6                                         018  001000 0 1111                                                                            0096          NME00                                             019  10 000011111                                                                             0097          BRNC    PDIS2                                     01A  10 000100001                                                                             0098          BRNC    LOVF1  ALWAYS BRANCH                      01B  000101 1 0000                                                                            0099  TOGF1   EXAM1                                             01C  0100000 0001                                                                             0100          AKNC    1                                         01D  000101 1 0000                                                                            0101          EXAM1                                             01E  001011 00000                                                                             0102          RETN                                              01F  011110 0 1111                                                                            0103  PDIS2   CMACD0  15                                        020  10 000010011                                                                             0104          BRNC    PDIS1                                     021  0000000 0001                                                                             0105  LOVF1   LKAC    1                                         022  0000101 1000                                                                             0106          LKRA    8                                         023  10 000110000                                                                             0107          BRNC    DIS4   ALWAYS BRANCH                      024  0000101 1000                                                                             0108  PIS1    LKRA    8                                         025  0000000 0000                                                                             0109          LKAC    0                                         026  011110 0 1111                                                                            0110          CMACD0  15                                        027  000100 0 0000                                                                            0111          MTOA0                                             028  001011 11000                                                                             0112          LOUT                                              029  001010 01111                                                                             0113          TSTKF                                             02A  10 000111100                                                                             0114          BRNC    DIS2                                      02B  000110 0 0111                                                                            0115          MTOAD0  7                                         02C  001011 00000                                                                             0116          RETN           THIS IS ONLY A NO OP               02D  0100010 1000                                                                             0117          AKAC    8                                         02E  10 001010010                                                                             0118          BRNC    DIS3                                      02F  0100010 0001                                                                             0119  DISOVF  AKAC    1                                         030  011111 0 0110                                                                            0120  DIS4    ATOMD0  6                                         031  0100111 0001                                                                             0121          AKRA    1                                         032  011110 0 1111                                                                            0122          CMACD0  15                                        033  000100 0 0000                                                                            0123          MTOA0                                             034  001011 11000                                                                             0124          LOUT                                              035  000110 1 1000                                                                            0125          MTOAD1  8                                         036  0100010 1000                                                                             0126          AKAC    8                                         037  000110 0 0110                                                                            0127          MTOAD0  6                                         038  001011 01000                                                                             0128          SMIN                                              039  0110100 1101                                                                             0129          CKRA    13                                        03A  10 000101111                                                                             0130          BRNC    DISOVF                                    03B  10 000100100                                                                             0131          BRNC    DIS1   ALWAYS BRANCN                      03C  0000000 0000                                                                             0132  DIS2    LKAC    0                                         03D  011111 0 0111                                                                            0133          ATOMD0  7                                         03E  001000 1 0100                                                                            0134          TSTF1   F3                                        03F  10 000101111                                                                             0135          BRNC    DISOVF                                    040  11 010010011                                                                             0136          CALL    THREE                                     041  11 000000000                                                                             0137          CALL    TOFFDIS                                   042  0000111 0000                                                                             0138  ADDC    LKAR    0                                         043  011111 1 0111                                                                            0139          ATOMD1  7                                         044  000100 1 0000                                                                            0140  ADDC1   MTOA1                                             045  0100010 1000                                                                             0141          AKAC    8                                         046  10 001001010                                                                             0142          BRNC    ADDC2                                     047  011101 1 0000                                                                            0143          ATOM1                                             048  0100111 0001                                                                             0144          AKRA    1                                         049  10 001000100                                                                             0145          BRNC    ADDC1  ALWAYS BRANCH                      04A  011101 1 0000                                                                            0146  ADDC2   ATOM1                                             04B  001011 00000                                                                             0147          RETN                                              04C  0110100 0111                                                                             0148          CKRA    7                                         04D  10 000100001                                                                             0149          BRNC    LOVF1                                     04E  11 001000010                                                                             0150  LOVF2   CALL    ADDC                                      04F  0110100 0111                                                                             0151          CKRA    7                                         05C  10 001001110                                                                             0152          BRNC    LOVF2                                     051  10 000100001                                                                             0153          BRNC    LOVF1  ALWAYS BRANCH                      052  0100010 1001                                                                             0154  DIS3    AKAC    9                                         053  011111 0 0111                                                                            0155          ATOMD0  7                                         054  0110000 0011                                                                             0156          CKAC    3      *** THIS IS THE TIME               055  10 000110000                                                                             0157          BRNC    DIS4   CONSTANT FOR                       056  11 000000000                                                                             0158          CALL    TOFFDIS                                                                               DEBOUNCE ***                       057  11 010010110                                                                             0159          CALL    EXBA                                      058  0000000 0000                                                                             0160          LKAC    0                                         059  11 000000101                                                                             0161          CALL    PUP1                                      05A  000100 0 0000                                                                            0162  CLF1    MTOAC                                             05B  0110000 1111                                                                             0163          CKAC    15                                        05C  10 001011111                                                                             0164          BRNC    CLF2                                      05D  0000000 0000                                                                             0165          LKAC    0                                         05E  011101 0 0000                                                                            0166          ATOM0                                             05F  0100111 0001                                                                             0167  CLF2    AKRA    1                                         060  10 001011010                                                                             0168          BRNC    CLF1                                      061  0000111 1101                                                                             0169          LKAR    13                                        062  001011 11000                                                                             0170          LOUT                                              063  0010100 0001                                                                             0171          TSTK    K1                                        064  10 000000000                                                                             0172          BRNC    TOFFDIS                                   065  0000101 1000                                                                             0173          LKRA    8                                         066  001000 1 0100                                                                            0174          TSTF1   F3                                        067  10 001101001                                                                             0175          BRNC    NOTOVF                                    068  10 110110101                                                                             0176          BRNC    LOCKB  ALWAYS BRANCH                      069  0010100 0100                                                                             0177  NOTOVF  TSTK    K3                                        06A  10 011001100                                                                             0178          BRNC    DIVIDE                                    06B  0000101 0011                                                                             0179          LKRA    3                                         06C  001011 11000                                                                             0180          LOUT                                              06D  0010100 0100                                                                             0181          TSTK    K3                                        06E  10 011001110                                                                             0182          BRNC    PLUS                                      06F  0010100 0001                                                                             0183  TK124   TSTK    K1                                        070  10 010010011                                                                             0184          BRNC    THREE                                     071  0010100 0010                                                                             0185          TSTK    K2                                        072  10 010010010                                                                             0186          BRNC    TWO                                       073  0010100 1000                                                                             0187          TSTK    K4                                        074  10 010010001                                                                             0188          BRNC    ONE                                       075  001011 00000                                                                             0189          RETN                                              076  0000101 0001                                                                             0190          LKRA    1                                         077  001011 11000                                                                             0191          LOUT                                              078  0010100 0100                                                                             0192          TSTK    K3                                        079  10 011001101                                                                             0193          BRNC    TIMES                                     07A  11 001101111                                                                             0194          CALL    TK124                                     07B  0110000 1101                                                                             0195          CKAC    13                                        07C  10 010010011                                                                             0196          BRNC    THREE                                     07D  0000101 0100                                                                             0197          LKRA    4                                         07E  001011 11000                                                                             0198          LOUT                                              07F  0010100 0100                                                                             0199          TSTK    K3                                        080  10 011011011                                                                             0200          BRNC    EQUALS                                    081  0010100 0001                                                                             0201          TSTK    K1                                        082  10 010010101                                                                             0202          BRNC    NUMENT                                    083  0000000 0000                                                                             0203          LKAC    0                                         084  0010100 0010                                                                             0204          TSTK    K2                                        085  10 010010101                                                                             0205          BRNC    NUMENT                                    086  0010100 1000                                                                             0206          TSTK    K4                                        087  10 010111001                                                                             0207          BRNC    CE                                        088  0000111 1010                                                                             0208          LKAR    10                                        089  001011 11000                                                                             0209          LOUT                                              08A  0010100 0100                                                                             0210          TSTK    K3                                        08B  10 010111111                                                                             0211          BRNC    MINUS                                     08C  11 001101111                                                                             0212          CALL    TK124                                     08D  C110000 1010                                                                             0213          CKAC    10                                        08E  10 010010011                                                                             0214          BRNC    THREE                                     08F  11 010010110                                                                             0215          CALL    EXBA                                      090  10 000010001                                                                             0216          BRNC    NOLOCK ALWAYS BRANCH                      091  0100010 1111                                                                             0217  ONE     AKAC    15                                        092  0100010 1111                                                                             0218  TWO     AKAC    15                                        093  0100010 0110                                                                             0219  THREE   AKAC    6                                         094  001011 00000                                                                             0220          RETN                                              095  011111 0 1001                                                                            0221  NUMENT  ATOMD0  9                                         096  0000101 0000                                                                             0222  EXBA    LKRA    0                                         097  000100 0 0000                                                                            0223  EXBA1   MTOA0                                             098  0100111 1000                                                                             0224          AKRA    8                                         099  000101 0 0000                                                                            0225          EXAM0                                             09A  0100111 1000                                                                             0226          AKRA    8                                         09B  011101 0 0000                                                                            0227          ATOM0                                             09C  0100111 0001                                                                             0228          AKRA    1                                         09D  0110100 1000                                                                             0229          CKRA    8                                         09E  10 010010111                                                                             0230          BRNC    EXBA1                                     09F  001011 00000                                                                             0231          RETN                                              0A0  001000 1 0001                                                                            0232          TSTF1   F1                                        0A1  10 010100100                                                                             0233          BRNC    NU1                                       0A2  11 000000101                                                                             0234          CALL    PUP1                                      0A3  011111 1 1000                                                                            0235          ATOMD1  8                                         0A4  0000101 1000                                                                             0236  NU1     LKRA    8                                         0A5  000110 0 0001                                                                            0237          MTOAD0  1                                         0A6  0110000 1101                                                                             0238          CKAC    13                                        0A7  10 010101011                                                                             0239          BRNC    NOTDPT                                    0A8  001000 1 0010                                                                            0240          TSTF1   F2                                        0A9  11 110110001                                                                             0241          CALL    TOGF2                                     0AA  10 000001111                                                                             0242          BRNC    LOCK   ALWAYS BRANCH                      0AB  000110 0 1101                                                                            0243  NOTDPT  MTOAD0  13                                        0AC  0110000 0000                                                                             0244          CKAC    0                                         0AD  10 000001111                                                                             0245          BRNC    LOCK                                      0AE  001000 1 0010                                                                            0246          TSTF1   F2                                        0AF  10 010110110                                                                             0247          BRNC    NU3                                       0B0  000110 0 1111                                                                            0248          MTOAD0  15                                        0B1  0110000 0101                                                                             0249          CKAC    5                                         0B2  10 010110100                                                                             0250          BRNC    NU4                                       0B3  10 000001111                                                                             0251          BRNC    LOCK   ALWAYS BRANCH                      0B4  0100010 0001                                                                             0252  NU4     AKAC    1                                         0B5  011111 0 1111                                                                            0253          ATOMD0  15                                        0B6  000110 0 0001                                                                            0254  NU3     MTOAD0  1                                         0B7  11 101000111                                                                             0255          CALL    SL1                                       0B8  10 000001111                                                                             0256          BRNC    LOCK                                      0B9  11 010010110                                                                             0257  CE      CALL    EXBA                                      0BA  000110 1 1000                                                                            0258          MTOAD1  8                                         0BB  001000 1 0001                                                                            0259          TSTF1   F1                                        0BC  11 000000100                                                                             0260          CALL    PUP                                       0BD  011111 1 1000                                                                            0261  CE1     ATOMD1  8                                         0BE  10 000001100                                                                             0262          BRNC    LOCK1  ALWAYS BRANCH                      0BF  001000 1 0001                                                                            0263  MINUS   TSTF1   F1                                        0C0  10 011001111                                                                             0264          BRNC    MIN1                                      0C1  0000101 1000                                                                             0265          LKRA    8                                         0C2  001000 1 0001                                                                            0266          TSTF1   F1                                        0C3  10 011001111                                                                             0267          BRNC    MIN1                                      0C4  0000101 1001                                                                             0268          LKRA    9                                         0C5  001000 1 0010                                                                            0269          TSTF1   F2                                        0C6  10 011001000                                                                             0270          BRNC    MIN2                                      0C7  10 011001111                                                                             0271          BRNC    MIN1                                      0C8  11 000000100                                                                             0272  MIN2    CALL    PUP                                       0C9  0000000 1000                                                                             0273          LKAC    8                                         0CA  011111 1 1000                                                                            0274          ATOMD1  8                                         0CB  10 000001111                                                                             0275          BRNC    LOCK                                      0CC  0100010 0100                                                                             0276  DIVIDE  AKAC    4                                         0CD  0100010 1111                                                                             0277  TIMES   AKAC    15                                        0CE  0100010 0101                                                                             0278  PLUS    AKAC    5                                         0CF  011111 1 1011                                                                            0279  MIN1    ATOMD1  11                                        0D0  11 000000000                                                                             0280          CALL    TOFFDIS                                   0D1  001000 1 1111                                                                            0281          NME01                                             0D2  10 101111000                                                                             0282          BRNC    PPOST                                     0D3  0000101 1001                                                                             0283          LKRA    9                                         0D4  001000 1 0010                                                                            0284          TSTF1   F2                                        0D5  10 011010111                                                                             0285          BRNC    NOTPOST                                   0D6  10 101111000                                                                             0286          BRNC    PPOST  ALWAYS BRANCH                      0D7  0000101 1000                                                                             0287  NOTPOST LKRA    8                                         0D8  001000 1 0001                                                                            0288          TSTF1   F1                                        OD9  10 011011110                                                                             0289          BRNC    PRENORM                                   0DA  10 101111000                                                                             0290          BRNC    PPOST  ALWAYS BRANCH                      0DB  11 000000000                                                                             0291  EQUALS  CALL    TOFFDIS                                   0DC  001000 1 1111                                                                            0292          MNE01                                             0DD  10 101111000                                                                             0293          BRNC    PPOST                                     0DE  11 010010110                                                                             0294  PRENORM CALL    EXBA                                      0DF  000110 0 1101                                                                            0295  PRE1    NTOAD0  13                                        0E0  0110000 0000                                                                             0296          CKAC    0                                         0E1  10 011101000                                                                             0297          BRNC    PRE2                                      0E2  11 101000110                                                                             0298          CALL    SL                                        0E3  000110 0 1111                                                                            0299          MTOAD0  15                                        0E4  0100010 0001                                                                             0300          AKAC    1                                         0E5  011111 0 1111                                                                            0301          ATOMD0  15                                        0E6  0110000 1010                                                                             0302          CKAC    10                                        0E7  10 011011111                                                                             0303          BRNC    PRE1                                      0E8  11 100010010                                                                             0304  PRE2    CALL    EXBC                                      0E9  11 101010011                                                                             0305          CALL    TOGF3                                     0EA  001000 1 0100                                                                            0306          TSTF1   F3                                        0EB  10 011101101                                                                             0307          BRNC    EXC1                                      0EC  10 011011111                                                                             0308          BRNC    PRE1   ALWAYS BRANCH                      0ED  0000101 1001                                                                             0309  EXC1    LKRA    9                                         0EE  001000 1 0010                                                                            0310          TSTF1   F2                                        0EF  10 011110001                                                                             0311          BRNC    EXSIGN1                                   0F0  10 011111001                                                                             0312          BRNC    EXC2   ALWAYS BRANCH                      0F1  0000101 1010                                                                             0313  EXSIGN1 LKRA    10                                        0F2  001000 1 1000                                                                            0314          TSTF1   F4                                        0F3  10 011110101                                                                             0315          BRNC    EXSIGN                                    0F4  11 011111111                                                                             0316          CALL    EXC4                                      0F5  000110 1 1001                                                                            0317  EXSIGN  MTOAD1  9                                         0F6  000111 1 1000                                                                            0318          EXAMD1  8                                         0F7  011111 1 1001                                                                            0319          ATOMD1  9                                         0F8  11 100010010                                                                             0320          CALL    EXBC                                      0F9  0000101 1010                                                                             0321  EXC2    LKRA    10                                        0FA  001000 1 0001                                                                            0322          TSTF1   F1                                        0FB  10 111001100                                                                             0323          BRNC    CTOA                                      0FC  000110 1 1001                                                                            0324          MTOAD1  9                                         0FD  0100010 1000                                                                             0325          AKAC    8                                         0FE  10 100000011                                                                             0326          BRNC    EXC3                                      0FF  0000000 1000                                                                             0327  EXC4    LKAC    8                                         100  010111 1 1000                                                                            0328          AMACD1  8                                         101  011111 1 1000                                                                            0329          ATOMD1  8                                         102  001011 00000                                                                             0330          RETN                                              103  001000 1 0100                                                                            0331  EXC3    TSTF1   F3                                        104  10 101011001                                                                             0332          BRNC    MULTIPLY                                  105  11 100010010                                                                             0333          CALL    EXBC                                      106  0000101 1000                                                                             0334  BZERO   LKRA    8                                         107  000100 0 0000                                                                            0335  BZERO1  MTOAD0                                            108  0110000 0000                                                                             0336          CKAC    0                                         109  10 100010001                                                                             0337          BRNC    BNZERO                                    10A  0100111 0001                                                                             0338          AKRA    1                                         10B  0110100 1111                                                                             0339          CKRA    15                                        10C  10 100000111                                                                             0340          BRNC    BZERO1                                    10D  001011 00000                                                                             0341          RETN                                              10E  011111 1 1000                                                                            0342          ATOMD1  8                                         10F  11 111001010                                                                             0343          CALL    MULT13                                    110  10 110110101                                                                             0344          BRNC    LOCKB                                     111  001011 00000                                                                             0345  BNZERO  RETN                                              112  0000101 0000                                                                             0346  EXBC    LKRA    0                                         113  000100 1 0000                                                                            0347  EXBC1   MTOA1                                             114  0100111 1000                                                                             0348          AKRA    8                                         115  000101 0 0000                                                                            0349          EXAM0                                             116  0100111 1000                                                                             0350          AKRA    8                                         117  011101 1 0000                                                                            0351          ATOM1                                             118  0100111 0001                                                                             0352          AKRA    1                                         119  0110100 1000                                                                             0353          CKRA    8                                         11A  10 100010011                                                                             0354          BRNC    EXBC1                                     11B  001011 00000                                                                             0355          RETN                                              11C  11 010010110                                                                             0356          CALL    EXBA                                      11D  0000101 1000                                                                             0357  SUBDPT  LKRA    8                                         11E  000110 1 0111                                                                            0358          MTOAD1  7                                         11F  0100000 1111                                                                             0359          AKNC    15                                        120  0100010 0001                                                                             0360          AKAC    1                                         121  10 100111101                                                                             0361          BRNC    SUBDPT1                                   122  000110 0 0111                                                                            0362          MTOAD0  7                                         123  001011 00000                                                                             0363  SUBDPT2 RETN                                              124  011111 0 1111                                                                            0364          ATOMDO  15                                        125  0000111 0000                                                                             0365  A-C=A   LKAR    0                                         126  010101 1 0000                                                                            0366  ADD1    AMAC1                                             127  0100000 1111                                                                             0367          AKNC    15                                        128  0100010 0001                                                                             0368          AKAC    1                                         129  10 100101011                                                                             0369          BRNC    ADD2                                      12A  10 100110011                                                                             0370          BRNC    ADD4   ALWAYS BRANCH                      12B  010101 0 0000                                                                            0371  ADD2    AMACO                                             12C  10 100110000                                                                             0372          BRNC    ADD3                                      12D  011101 0 0000                                                                            0373          ATOM0                                             12E  0000000 0000                                                                             0374          LKAC    0                                         12F  10 100110011                                                                             0375          BRNC    ADD4   ALWAYS BRANCH                      130  0100010 1010                                                                             0376  ADD3    AKAC    10                                        131  011101 0 0000                                                                            0377          ATOM0                                             132  0000000 0001                                                                             0378          LKAC    1                                         133  0100111 0001                                                                             0379          ADD4    AKRA   1                                  134  0110100 0111                                                                             0380          CKRA    7                                         135  10 100100110                                                                             0381          BRNC    ADD1                                      136  001011 00000                                                                             0382          RETN                                              137  0110000 0000                                                                             0383          CKAC    0                                         138  10 101000000                                                                             0384          BRNC    DIV1                                      139  000110 0 1000                                                                            0385          MTOAD0  8                                         13A  0100010 0001                                                                             0386          AKAC    1                                         13B  011111 0 1000                                                                            0387          ATOMD0  8                                         13C  10 100100101                                                                             0388          BRNC    A-C=A  ALWAYS BRANCH                      13D  010111 0 0111                                                                            0389  SUBDPT1 AMACD0  7                                         13E  11 101010011                                                                             0390          CALL    TCGF3                                     13F  10 100100011                                                                             0391          BRNC    SUBDPT2                                                                               ALWAYS BRANCH                      140  000110 0 1101                                                                            0392  DIV1    MTOAD0  13                                        141  0110000 0000                                                                             0393          CKAC    0                                         142  10 101111001                                                                             0394          BRNC    POSTNORM                                  143  11 101100011                                                                             0395          CALL    A+C=A                                     144  11 101000110                                                                             0396          CALL    SL                                        145  11 010010110                                                                             0397          CALL    EXBA                                      146  0000000 0000                                                                             0398  SL      LKAC    0                                         147  0000101 1000                                                                             0399  SL1     LKRA    8                                         148  000101 0 0000                                                                            0400  SL2     EXAM0                                             149  0100111 0001                                                                             0401          AKRA    1                                         14A  0110100 1111                                                                             0402          CKRA    15                                        14B  10 101001000                                                                             0403          BRNC    SL2                                       14C  001011 00000                                                                             0404          RETN                                              14D  11 010010110                                                                             0405          CALL    EXBA                                      14E  000110 0 1111                                                                            0406          MTOAD0  15                                        14F  0100010 0001                                                                             0407          AKAC    1                                         150  10 101010111                                                                             0408          BRNC    DIV4                                      151  001000 1 0100                                                                            0409          TSTF1   F3                                        152  10 110001110                                                                             0410          BRNC    UNDERFL                                   153  000101 1 0000                                                                            0411  TOGF3   EXAM1                                             154  0100000 0100                                                                             0412          AKNC    4                                         155  000101 1 0000                                                                            0413          EXAM1                                             156  001011 00000                                                                             0414          RETN                                              157  011111 0 1111                                                                            0415  DIV4    ATOMD0  15                                        158  10 100100101                                                                             0416          BRNC    A-C=A  ALWAYS BRANCH                      159  000110 1 0111                                                                            0417  MULTIPLY                                                                               MTOAD1  7                                         15A  010111 0 1111                                                                            0418          AMACD0  15                                        15B  10 101011110                                                                             0419          BRNC    MUL3                                      15C  0000101 1001                                                                             0420          LKRA    9                                         15D  11 101010011                                                                             0421          CALL    TOGF3                                     15E  011111 0 0111                                                                            0422  MUL3    ATOMD0  7                                         15F  000110 0 1000                                                                            0423  MUL4    MTOAC0  8                                         160  0100010 1111                                                                             0424          AKAC    15                                        161  10 101110101                                                                             0425          BRNC    MULT1                                     162  011111 0 1000                                                                            0426          ATOMD0  8                                         163  0000111 0000                                                                             0427  A+C=A   LKAR    0                                         164  010101 1 0000                                                                            0428  ADD6    AMAC1                                             165  010101 0 0000                                                                            0429          AMAC0                                             166  10 101101011                                                                             0430          BRNC    ADD7                                      167  0100010 0110                                                                             0431          AKAC    6                                         168  011101 0 0000                                                                            0432  ADD8    ATOM0                                             169  0000000 0001                                                                             0433          LKAC    1                                         16A  10 101110000                                                                             0434          BRNC    ADD10  ALWAYS BRANCH                      16B  011101 0 0000                                                                            0435  ADD7    ATOM0                                             16C  0100010 0110                                                                             0436          AKAC    6                                         16D  10 101101111                                                                             0437          BRNC    ADD9                                      16E  10 101101000                                                                             0438          BRNC    ADD8   ALWAYS BRANCH                      16F  0000000 0000                                                                             0439  ADD9    LKAC    0                                         170  0100111 0001                                                                             0440  ADD10   AKRA    1                                         171  0110100 0111                                                                             0441          CKRA    7                                         172  10 101100100                                                                             0442          BRNC    ADD6                                      173  001011 00000                                                                             0443          RETN                                              174  10 101011111                                                                             0444          BRNC    MUL4   ALWAYS BRANCH                      175  11 100000110                                                                             0445  MULT1   CALL    BZERO                                     176  0110000   0000  0446            CKAC   0                                  177  10 110110111                                                                             0447          BRNC    MULT10                                    178  11 010010110                                                                             0448  PPOST   CALL    EXBA                                      179  0000101 1110                                                                             0449  POSTNORM                                                                               LKRA    14                                        17A  001000 0 1111                                                                            045C          MNE00                                             17B  10 110000011                                                                             0451          BRNC    PNORM1                                    17C  11 110111001                                                                             0452          CALL    SR                                        17D  000110 0 1111                                                                            0453          MTOAD0  15                                        17E  0100010 1111                                                                             0454          AKAC    15                                        17F  011111 0 1111                                                                            0455          ATOMD0  15                                        180  0110000 1111                                                                             0456          CKAC    15                                        181  10 110000011                                                                             0457          BRNC    PNORM1                                    182  11 111001010                                                                             0458          CALL    MULT13                                    183  0000101 1000                                                                             0459  PNORM1  LKRA    8                                         184  001000 1 0100                                                                            0460          TSTF1   F3                                        185  10 110001010                                                                             0461          BRNC    POSTN                                     186  000110 0 1111                                                                            0462          MTOAD0  15                                        187  0100010 0110                                                                             0463          AKAC    6                                         188  011111 0 1111                                                                            0464          ATOMD0  15                                        189  10 000001111                                                                             0465          BRNC    LOCK   ALWAYS BRANCH                      18A  0000101 1001                                                                             0466  POSTN   LKRA    9                                         18B  001000 1 0100                                                                            0467          TSTF1   F3                                        18C  10 110001111                                                                             0468          BRNC    PNORM2                                    18D  11 101010011                                                                             0469          CALL    TOGF3                                     18E  11 000000100                                                                             0470  UNDERFL CALL    PUP                                       18F  000110 0 1111                                                                            0471  PNORM2  MTOAD0  15                                        190  0100010 1010                                                                             0472          AKAC    10                                        191  10 110010110                                                                             0473          BRNC    PNORM3                                    192  0100010 0101                                                                             0474  PNORM6  AKAC    5                                         193  011111 0 1111                                                                            0475          ATOMD0  15                                        194  11 110111001                                                                             0476          CALL    SR                                        195  10 110001111                                                                             0477          BRNC    PNORM2 ALWAYS BRANCH                      196  0110000 1010                                                                             0478  PNORM3  CKAC    10                                        197  10 110011001                                                                             0479          BRNC    PNORM4                                    198  10 110011100                                                                             0480          BRNC    PNORM5 ALWAYS BRANCH                      199  0000101 1000                                                                             0481  PNORM4  LKRA    8                                         19A  001000 0 1111                                                                            0482          MNE00                                             19B  10 110010010                                                                             0483          BRNC    PNORM6                                    19C  11 100000110                                                                             0484  PNORM5  CALL    BZERO                                     19D  0110000 0000                                                                             0485          CKAC    0                                         19E  10 110100000                                                                             0486          BRNC    PNORM7                                    19F  011111 1 1000                                                                            0487          ATOMD1  8                                         1A0  0000000 0000                                                                             0488  PNORM7  LKAC    0                                         1A1  000111 1 1011                                                                            0489          EXAMD1  11                                        1A2  0110000 0000                                                                             0490          CKAC    0                                         1A3  10 110101000                                                                             0491          BRNC    FUNCKEY                                   1A4  0000101 1001                                                                             0492          LKRA    9                                         1A5  001000 1 0010                                                                            0493          TSTF1   F2                                        1A6  11 110110001                                                                             0494          CALL    TOGF2                                     1A7  10 000001100                                                                             0495          BRNC    LOCK1                                     1A8  011111 1 1010                                                                            0496  FUNCKEY ATOMD1  10                                        1A9  11 100010010                                                                             0497          CALL    EXBC                                      1AA  11 000000100                                                                             0498          CALL    PUP                                       1AB  11 111001100                                                                             0499          CALL    CTOA                                      1AC  000110 1 1000                                                                            0500          MTOAD1  8                                         1AD  011111 1 1001                                                                            0501          ATOMD1  9                                         1AE  0000101 1001                                                                             0502          LKRA    9                                         1AF  001000 1 0010                                                                            0503          ATOMD0  F2                                        1B0  10 110110101                                                                             0504          BRNC    LOCKB                                     1B1  000101 1 0000                                                                            0505  TOGF2   EXAM1                                             1B2  0100000 0010                                                                             0506          AKNC    2                                         1B3  000101 1 0000                                                                            0507          EXAM1                                             1B4  001011 00000                                                                             0508          RETN                                              1B5  11 010010110                                                                             0509  LOCKB   CALL    EXBA                                      1B6  10 000001100                                                                             0510          BRNC    LOCK1  ALWAYS BRANCH                      1B7  11 110111001                                                                             0511  MULT10  CALL    SR                                        1B8  11 010010110                                                                             0512          CALL    EXBA                                      1B9  0000000 0000                                                                             0513  SR      LKAC    0                                         1BA  0000101 1110                                                                             0514          LKRA    14                                        1BB  000101 0 0000                                                                            0515  SR1     EXAM0                                             1BC  0100111 1111                                                                             0516          AKRA    15                                        1BD  0110100 0111                                                                             0517          CKRA    7                                         1BE  10 110111011                                                                             0518          BRNC    SR1                                       1BF  001011 00000                                                                             0519          RETN                                              1C0  11 010010110                                                                             0520          ATOMD0  EXBA                                      1C1  000110 0 0111                                                                            0521  SUB1DPT MTOAD0  7                                         1C2  0100010 1111                                                                             0522          AKAC    15                                        1C3  10 111000101                                                                             0523          BRNC    MULT11                                    1C4  10 101011110                                                                             0524          BRNC    MUL3   ALWAYS BRANCH                      1C5  0000101 1001                                                                             0525  MULT11  LKRA    9                                         1C6  001000 1 0100                                                                            0526          TSTF1   F3                                        1C7  10 111001010                                                                             0527          CALL    MULT13                                    1C8  11 101010011                                                                             0528  MULT12  CALL    TOGF3                                     1C9  10 101011110                                                                             0529          BRNC    MUL3   ALWAYS BRANCH                      1CA  0000101 1000                                                                             0530  MULT13  LKRA    8                                         1CB  10 111001000                                                                             0531          BRNC    MULT12 ALWAYS BRANCH                      1CC  000110 1 0111                                                                            0532  CTOA    MTCAD1  7                                         1CD  011111 0 0111                                                                            0533          ATOMDO  7                                         1CE  11 101100011                                                                             0534          CALL    A+C=A                                     1CF  000110 1 1001                                                                            0535          MTOAD1  9                                         1DC  011111 1 0110                                                                            0536          ATOMD1  6                                         1D1  11 100010010                                                                             0537  PLMI1   CALL    EXBC                                      1D2  11 100011101                                                                             0538  PLMI2   CALL    SUBDPT                                    1D3  001000 1 0100                                                                            0539          TSTF1   F3                                        1D4  10 111011111                                                                             0540          BRNC    PLMI3                                     1D5  11 101010011                                                                             0541          CALL    TOGF3                                     1D6  11 011110101                                                                             0542          CALL    EXSIGN                                    1D7  11 010010110                                                                             0543          CALL    EXBA                                      1D8  10 111010001                                                                             0544          BRNC    PLMI1  ALWAYS BRANCH                      1D9  11 010010110                                                                             0545  PLMI4   CALL    EXBA                                      1DA  11 110111001                                                                             0546          CALL    SR                                        1DB  11 010010110                                                                             0547          CALL    EXBA                                      1DC  0100010 1111                                                                             0548          AKAC    15                                        1DD  011111 0 0111                                                                            0549          ATOMD0  7                                         1DE  10 111010010                                                                             0550          BRNC    PLMI2  ALWAYS BRANCH                      1DF  0110000 0000                                                                             0551  PLMI3   CKAC    0                                         1E0  10 111011001                                                                             0552          BRNC    PLMI4                                     1E1  000110 1 1000                                                                            0553          MTOAD1  8                                         1E2  010111 1 1001                                                                            0554          AMACD1  9                                         1E3  10 111100110                                                                             0555          BRNC    PLMI5                                     1E4  11 101100011                                                                             0556  PLMI6   CALL    A+C=A                                     1E5  10 111101101                                                                             0557          BRNC    PLMI8  ALWAYS BRANCH                      1E6  0100010 1000                                                                             0558  PLMI5   AKAC    8                                         1E7  10 111100100                                                                             0559          BRNC    PLMI6                                     1E8  11 011110101                                                                             0560  PLMI7   CALL    EXSIGN                                    1E9  11 100010010                                                                             0561          CALL    EXBC                                      1EA  11 100100101                                                                             0562          CALL    A-C=A                                     1EB  0110000 0000                                                                             0563          CKAC    0                                         1EC  10 111110010                                                                             0564          BRNC    PLMI9                                     1ED  11 100010010                                                                             0565  PLMI8   CALL    EXBC                                      1EE  0000000 0000                                                                             0566          LKAC    0                                         1EF  000111 1 0110                                                                            0567          EXAMD1  6                                         1F0  011111 1 1001                                                                            0568          ATOMD1  9                                         1F1  10 101111000                                                                             0569          BRNC    PPOST  ALWAYS BRANCH                      1F2  11 101100011                                                                             0570  PLMI9   CALL    A+C=A                                     1F3  11 010010110                                                                             0571          CALL    EXBA                                      1F4  11 100010010                                                                             0572          CALL    EXBC                                      1F5  11 010010110                                                                             0573          CALL    EXBA                                      1F6  10 111101000                                                                             0574          BRNC    PLMI7  ALWAYS BRANCH                      __________________________________________________________________________

A calculator system embodying the present invention has now been described in detail. It is anticipated that various modifications may be made to the described system such as increasing its bit capacity, modifying, increasing, or decreasing the instruction set given by way of example in Table I in order to perform other functions and/or modifying, increasing or decreasing the specific program steps stored in ROM 20A as given by way of example in Table II in order to cause the system to operate in a different manner.

In addition, the preferred embodiment has been described as utilizing I² L circuitry; however, it is contemplated that one of ordinary skill in the art could easily fabricate the same circuitry utilizing other bipolar technology, metal insulator semiconductor technology, CMOS technology, etc.

Since it is obvious that many additional changes and modifications can be made in the above described details without departing from the nature and spirit of the invention, it is understood that the invention is not to be limited to said details except as set forth in the appended claims. 

What is claimed is:
 1. An electronic calculator system comprising:a. data storage means; b. control circuitry including an instruction storage means for providing multi-bit command signals which define the operations of the system; c. an arithmetic unit for performing operations on data including data stored in said data storage means and data stored in said instruction storage means, said arithmetic unit including a plurality of single bit adder sections with each of said adder sections for adding two input bits and an input carry bit from a previous adder section to produce an output sum bit and an output carry bit to a next adder section; d. means coupling a plurality of selected bits of said instruction storage means as input bits to said arithmetic unit; e. means coupling first selected bits of said data storage means as input bits to said arithmetic unit and f. controllable logic means including a plurality of logical AND functioning gates each having first and second inputs and an output, the first input and output of each said logical AND functioning gates respectively coupling the carry output bit from a previous adder section as the carry input bit of a next adder section with the second input of each of said locical AND functioning gates connected in common to another selected bit of said instruction storage means for selectively enabling or disabling the carry bits from section to section in accordance with the state of said another selected bit, said control circuitry being arranged to provide toggle commands from said instruction storage means for selectively toggling one or more individual bits in said arithmetic unit wherein each of said toggle commands include said another bit set in a state for said logic means to disable the carry bits from section to section and said first selected bits set to states indicative of the specific ones of said selected bits to be toggled.
 2. The electronic calculator system according to claim 1 wherein said one of toggle commands is a complement data command and wherein said first selected bits of said complement data command are all set to ones which are added to the data in said arithmetic unit with said logic means controlled by said another selected bit to disable the carries from section to section.
 3. An electronic calculator system comprising:a. data storage means; b. control circuitry including an instruction storage means for providing command signals which define the operations of the system; c. an arithmetic unit for performing operations on data including data stored in said data storage means, said arithmetic unit including a plurality of single bit adder sections with each of said adder sections for adding two input bits and an input carry bit from a previous section to produce an output sum bit and an output carry bit to a next section; and d. controllable logic means including a respective plurality of logical AND functioning gates each having first and second inputs and an output, the first input and output of each of said logical AND functioning gates respectively coupling the carry output bit from a previous adder section as the carry bit of a next adder section with the second input of each of said logical AND functioning gates connected in common to said control circuitry for receiving said command signals and for simultaneously selectively enabling or disabling the carry bits from section to section in accordance with said command signals, said control circuitry being arranged to provide flag toggle commands for selectively toggling one or more individual bit flags indicative of the state of said system wherein each of said flag toggle commands include an indicator bit for said logic means to disable the carries from section to section and a plurality of other bits indicative of the specific ones of said bit flags to be toggled.
 4. The electronic calculator system according to claim 3 wherein at least one of said command signals is comprised of bits output from said instruction storage means and wherein a selected one of said bits comprises said indicator bit which is applied directly to the second inputs of said logical AND functioning gates connected in common, and wherein said other bits of said at least one command signal are added directly to bit flags in said arithmetic unit to perform said toggle function.
 5. The electronic calculator system according to claim 3 wherein each single bit adder section of said arithmetic unit includes first and second half adder stages with the first stage for adding two input bits to produce a sum bit and the second stage for adding a carry output bit from a previous section to the sum bit from the first stage to produce the output sum bit and the carry output bit to the next section.
 6. An electronic calculator system comprising:a. data storage means; b. control circuitry including an instruction storage means for providing command signals which define the operations of the system; c. an arithmetic unit for performing operations on data including data stored in said data storage means, said arithmetic unit including a plurality of single bit adder sections with each of said adder sections for adding two input bits and an input carry bit from a previous section to produce an output sum bit and an output carry bit to a next section; and d. controllable logic means including a respective plurality of logical AND functioning gates each having first and second inputs and an output the first input and output of each of said logical AND functioning gates respectively coupling the carry output bit from a previous adder section as the carry input bit of a next adder section with the second input of each of said logical AND functioning gates connected in common to said control circuitry for receiving said command signals and for simultaneously selectively enabling or disabling the carry bits from section to section in accordance with said command signals, said control circuitry being arranged to cause said arithmetic unit to complement data by adding ones to said data with said logic means controlled to disable the carries from section to section.
 7. The electronic calculator system according to claim 6 wherein at least one of said command signals is comprised of bits output from said instruction storage means and wherein a selected one of said bits comprises an indicator bit which is applied directly to the second inputs of said logical AND functioning gates connected in commin, and wherein said other bits of said at least onc command signal are added directly to bit flags in said arithmetic unit to perform said complement data function.
 8. The electronic calculator system according to claim 6 wherein each single bit adder section of said arithmetic unit includes first and second half adder stages with the first stage for adding two input bits to produce a sum bit and the second stage for adding a carry output bit from a previous section to the sum bit from the first stage to produce the output sum bit and the carry output bit to the next section.
 9. The electronic calculator system according to claim 6 wherein selected bits from said instruction storage means containing all ones are provided to said arithmetic unit to complement said data.
 10. An electronic calculator comprising:a. keyboard means for inputting numeric and functional data to said calculator; b. control circuitry including an instruction storage means for providing command signals which define the operations of said calculator; c. data storage means; d. an arithmetic unit for performing operations on data including data stored in said data storage means, said arithmetic unit including a plurality of single bit adder sections with each of said adder sections for adding two input bits and an input carry bit from a previous section to produce an output sum bit and an output carry bit to a next section; e. controllable logic means including a respective plurality of logical AND functioning gates, each having an output and a first input for coupling the carry output bit from the previous section as the carry input bit of the next section and a second input connected in common to a selected bit output from said instruction storage means for selectively enabling or disabling all of the carry bits from section to section in accordance with the state of the selected bit of the command signals from said control circuitry, said control circuitry being arranged to provide flag toggle commands for individually toggling single bit flags indicative of the state of said calculator wherein each of said flag toggle commands include an indicator bit for said logic means to disable the carries from section to section; and f. display means for displaying data as calculated by said arithmetic unit under control of said control circuitry.
 11. The electronic calculator according to claim 10 wherein said single bit flags are individually toggled by adding other selected bits of said flag toggle commands to flag data stored in said data storage means in said arithmetic unit with said carries disabled.
 12. An electronic calculator comprising:a. keyboard means for inputting numeric and function data to said calculator; b. control circuitry including an instruction storage means for providing command signals which define the operations of the calculator; c. data storage means; d. an arithmetic unit for performing operations on data including data stored in said data storage means, said arithmetic unit including a plurality of single bit adder sections with each of said adder sections for adding two input bits and an input carry bit from a previous section to produce an output sum bit and an output carry bit to a next section; e. controllable logic means including a respective plurality of logical AND functioning gates each having first and second inputs and an output, the first input and output of each of said AND gates respectively coupling the carry output bit from a previous section as the carry input of a next section with the second inputs of each of said logical AND functioning gates connected to common to a selected bit output from said instruction storage means for selectively enabling or disabling all of the carry bits from section to section in accordance with the state of the selected bits of the command signals from said control circuitry, said control circuitry being arranged to cause said arithmetic unit to complement data in response to selected commands stored in said instruction storage means by adding ones to said data wherein said selected commands include an indicator bit for said logic means to disable the carries from section to section; and f. display means for displaying data as calculated by said arithmetic unit under control of said control circuitry.
 13. The electronic calculator according to claim 12 wherein the ones provided to said arithmetic unit for complementing data are provided as selected bits of said selected commands from said instruction storage means. 